Without limiting the scope of the invention, its background is described in connection with surface distress measurement system, method and apparatus, as an example.
Surfaces, e.g., such as pavement, roads, walkways, carriageways, parking lots, sidewalks and foundations, and the like are subject to heavy wear from traffic and/or environmental conditions. Over time, cracks cause the degradation of the pavement conditions and of the underlying surface. The increase in traffic on the nation's highways and the increasing weight of both commercial and individual vehicles has lead to an accelerated deterioration of the nation's road and highway infrastructure.
Pavement durability is affected by a number of factors, including: asphalt composition, construction techniques, number and speed of vehicles, overall weight and axle weight of vehicles that use the roadway, temperature and other environmental factors. Therefore, pavement conditions must be monitored to focus repairs on areas of greatest need. Furthermore, pavement conditions must be monitored so that a maintenance program may be established and areas prioritized based on need.
Many pavements, roads and parking lots were designed for low traffic volumes and have a thin bituminous surface. These surfaces are particularly susceptible to environmental conditions. For example, during wet weather, cracks in the surface of the pavement allow the force of traffic to inject water into the crack and under the pavement. Water under the pavement leads to erosion and eventually to failure of the pavement. Another related problem is the formation of frost heaves. In colder regions, the water under the pavement expands as it freezes and expands in the pavement creating a bump or “frost heave” that causes pavement failure. The detection of these cracks before they become extensive allows the sealing of the surface and in turn preserves pavement durability.
There are many other sources of pavement defects that affect the surface and serve as indicators of the general condition of the pavement. If these defects are detected early enough intervention to seal or repair them can be preformed before the defects develop into a more serious and expensive problems. Generally, when cracks reach a certain size remedial surface treatments are not effective therefore it is imperative that cracks are detected early and preferably when they are no larger than 1 mm. Another pavement defect is rutting, which is the result of surface deformation in the wheel path of the vehicle. Again, if these areas can be identified during the early stages preventive maintenance can be performed.
For reliable evaluation of the pavement conditions virtually every section of the road surface must be examined for crack, hairline cracks, holes and other defects that eventually lead to serious problems for vehicles. One method of evaluating the condition of the pavement is visual inspection of the pavement surface by skilled personnel, which is extremely labor intensive and suffer from the influence of human subjectivity. Therefore, the information obtained from the visual inspection of the pavement may not contain the detail necessary to accurately determine the condition of the pavement. Human evaluation of the conditions of the surface also leads to reproducibility problems for information on pavement cracking for common types of payment surfaces. Furthermore, for the visual inspection method is rate limited by the individual (e.g., time, speed, eyesight, environmental conditions and the like) and the very nature of this inspection exposes the individual to numerous traffic and safety hazards. Thus, it is virtually impossible for visual inspections of all sections of the roads in a particular municipality and/or region to gather, store, catalog and update the necessary crack data.
Automated measurement systems used to detect condition of the pavement include a video camera, which films the road surface at relatively high speeds. The video image is then processed to extrapolate data to determine the severity and extent of cracking. A computer evaluates the roughness profile and assessment of pavement surface condition, e.g., rutting, texture and cracking. Once cracks and/or defects reach a certain size, they are marked for repair. However, the current video systems are not without limitations. For example, these systems are prone to overlap and may also lack the definition necessary to evaluate the pavement surface for the initial stages of defect formation. Another problem associated with the detection of cracks in the surface is definition of the sensor when the image of the surface is large in comparison to the defect area, as the dimension of the defects may become of the order of a pixel or even smaller than a pixel. Therefore, the detection defects will become very difficult or highly random, particularly due to the analog-digital conversion that is necessary to process the image.
The automated measurement systems used to evaluate pavement conditions also include video logging to sensors (e.g., laser or ultrasound). However, these systems do not provide sufficient data relating to cracks. Many automated systems have limitations in their ability to discern cracks at the initial stages, in particular, they lack the ability to discern cracks on pavement surfaces from other structures and/or discern cracks from sealed areas on pavement surfaces. Furthermore, many systems are not functional at highway speeds, which is necessary for safety and efficient monitoring. Another limitation of the present automated measurement systems is the reliance on post processing of the data, which often is preformed manually and is susceptible to human error, reproducibility issues and is extremely labor intensive.
The foregoing problems have been recognized for many years and while numerous solutions have been proposed, none of them adequately address all of the problems in a single device, e.g., early detection of relatively small cracks in the early stage of formation, while reducing overlap and reliance on human judgment and improving resolution while allowing monitoring at highway speeds.